The present invention relates generally to a paint stripper composition and formulation, and more specifically to such a formulation which functions as an organic coating remover particularly adapted for use on non-ferrous metallic substrates. The formulation of the present invention is particularly desirable for use in the work place since it is nonhalogenated, property, is relatively nonvolatile under normal ambient conditions, and also possesses a reasonably useful and high flash point.
At the present time, formulations and methods for removal of organic coatings from metallic substrates usually involve one or more of the following techniques:
1. Chemical removal: PA1 2. Mechanical removal: PA1 (3. Thermal removal: PA1 (1) the chemical formulation employed is toxic; PA1 (2) the formulation is corrosive, particularly upon contact with non-ferrous metals; PA1 (3) alterations in surfaces and/or dimensions in articles may occur due to chemical and/or mechanical abrasion; PA1 (4) possible distortion of metallic articles occurring during exposure to conditions found in burn-off ovens, or from immersion in high temperature molten-salt baths; and/or PA1 (5) the extremely high cost of the use of cryogenic techniques.
(a) use of halogenated solvent-based stripper requiring either immersion or brush-on application. Such strippers are either: PA2 (b) use of aqueous sodium hydroxide solutions with high boiling point additives in immersion systems. In these applications, both temperatures typically range from between 200.degree. F.-250.degree. F. PA2 (a) use of high-pressure surface blasting with abrasive media, such as sand-blasting or the like. PA2 (a) use of high temperature burn-off ovens; PA2 (b) use of molten salt baths; PA2 (c) use of cryogenic materials and techniques.
(1) organic acid activated;
(2) neutral; or
(3) alkaline activated;
While these methods have been found effective in the removal of organic coatings from metallic articles, their use in connection with or upon non-ferrous metallic substrates is extremely limited. For example, the following characteristics and/or properties of materials utilized and the techniques employed frequently include the following:
For economic reasons, therefore, a common practice in industry is to scrap rejected painted non-ferrous parts and thereafter re-melt the material forming the article to reform it as a new article. Frequently the melting of rejected painted non-ferrous metallic articles is less expensive than exposure to a high quality stripping operation.
The present invention is useful for the treatment of rejected painted parts, particularly when melting is either impractical or cannot be undertaken on a cost-effective basis. This is of particular concern when dealing with parts and/or components having strict dimensional tolerances, or when the article may be applied in areas where hydrogen embrittlement will cause stress fracturing when the part or component is subjected to significant pressure gradients. Furthermore, the presently utilized techniques are found to be impractical whenever exposure to alloy forming materials (smut formation) is undesirable.
With regard to chemical removal of organic coatings from metallic articles, methylene chloride based formulations are presently commonly used. However, methylene chloride is now considered to be an undesirable material, and the United States Environmental Protection Agency has characterized the material as having possible carcinogenic effects in humans. Furthermore, methylene chloride has been listed by the Agency as a Total Toxic Organic and as such, its presence in rinse waters cannot be permitted to exceed 2.13 ppm. As a chlorinated solvent, methylene chloride is further harmful to the environment and may ultimately cause depletion of the ozone layer. The American Conference of Governmental Industrial Hygienists (ACIGH) has established a threshold limit value (TLV) of 50 ppm for this material. Additionally, the Occupational Safety Hazard Association (OSHA) has established a lower permissible exposure level (PEL) of only 500 ppm. Accordingly, it is anticipated that the use of methylene chloride will be more highly restricted in the future.
Methylene chloride strippers or coating removers are typically activated by relatively low molecular weight organic acids such as formic acid, acetic acid, and propionic acid. These materials typically have a very noxious odor, and have been given low TLV values as established by the ACIGH, and low PEL values as established by OSHA. These values currently are as follows:
______________________________________ Organic Acid ACIGH TLV (ppm) OSHA PEL (ppm) ______________________________________ Formic acid 5 5 Acetic acid 10 10 Propionic acid 10 Not established Cresylic acid 5 5 ______________________________________
Furthermore, these organic acids may attack the surfaces of certain non-ferrous metallic substrates, and as such, are deemed undesirable. Subsequent application of the articles or parts so treated may result in hydrogen embrittlement, substrate deterioration, or changes in dimensional tolerances, as well as exposure to certain alloy-forming components.
Certain methylene chloride based stripper formulations are alkaline activated. The most common alkaline component in such strippers is either ammonium hydroxide or a volatile organic amine such as ethylenediamine. Both ammonium hydroxide and ethylenediamine emit toxic fumes and have been assigned low TLV values and low PEL values by ACIGH and OSHA, respectively. Additionally, exposure of articles fabricated from brass may suffer from stress corrosion cracking upon exposure to amines. The TLV and PEL values as established by the relevant governmental agencies and assigned to these components are as follows:
______________________________________ ACIGH Alkaline Activator TLV (ppm) OSHA PEL (ppm) ______________________________________ Ammonium hydroxide 25 50 Ethylenediamine 10 10 ______________________________________
The fumes emitted by formulations containing ammonium hydroxide or ethylenediamine are both noxious and toxic. Thus, their use is limited in an industrial setting, and in the future may become even more limited.